Not quite a bomb: McMaster professor explains what fell at Halifax Harbour

The Fairview cargo terminal was a site of activity March 13, after four containers of uranium hexafluoride dropped six metres (Grace Kennedy / Peninsula News)

For most people the term radiation throws up red flags. Chernobyl, Fukushima, Nagasaki – all invoke images of the invisible cloud of radiation that permeates the human body. John Luxat, expert in Nuclear Safety Analysis at McMaster University in Hamilton, Ont., says it’s important to remember that the accident at Halifax Harbour on March 13 was much more benign.

“Had it been some other chemical, a potentially corrosive chemical such as chlorine, it would have been, ‘ah, chlorine. Yeah. No. Not a big problem.’ But this is radioactive,” Luxat says, “the word radioactive tends to get people worried.”

Late in the evening on March 13, four containers containing uranium hexafluoride dropped about six metres while they were being lifted off the “Atlantic Companion” at the Ceres terminal in Halifax’s north end. Workers were evacuated and tested for radiation, while fire crews took readings of the background radiation aboard the ship, which was four times higher than normal. This, Luxat says, is a normal reading considering the increased concentration of radioactive material in the containers.

What fell?

This radioactive material, the uranium hexafluoride, is the form of uranium used to create the enriched uranium necessary for nuclear reactors.

Uranium is predominately made up of two different isotopes, or types of uranium. There is the heavier isotope, uranium 238 which makes up about 99.3 per cent of all natural uranium. The other isotope, uranium 235, is only about 0.7 per cent and is responsible for fission, which creates the energy of a nuclear reaction.

In order for uranium to be useful in nuclear reactions, the uranium 235 content has to be increased to between 3.5 and five per cent. This is commonly done by heating uranium hexafluoride – a combination of natural uranium and fluoride gas – to very high temperatures and spinning it in a centrifuge. Because of the weight difference between the isotopes, the heavier, non-fissile atoms will move to the outside of the centrifuge, allowing researchers to collect the more reactive gas in the centre.

Under ordinary temperatures, uranium hexafluoride is in a solid state. It would have to be heated to at least 56 degrees Celsius, according to Luxat, in order to become the feared gas that could spread radiation. By way of comparison, the hottest day ever recorded in Osoyoos, B.C. – part of Canada’s only desert – was 42.8 degrees Celsius according to the Sunny Osoyoos website.

“Even in the worst cases would be if you release the contents and you heated them, say there was a fire and it got released, then it would be dispersed,” Luxat says, “but the concentrations would be extremely low. So in terms of the actual physical hazards, it would be insignificant.”

What could have happened?

(Grace Kennedy / Peninsula News)

The more worrying scenario that Halifax could have had to deal with, Luxat says, would have been if the containers had leaked and the contents had interacted with water. The “chemical toxicity” of uranium hexafluoride, according to the Canadian Nuclear Safety Commission, is a much larger hazard than its radioactivity.

When uranium hexafluoride interacts with water – even humid air will do – it “decomposes,” as Luxat put it, into two substances: small solid particles called uranyl fluoride, and fluoric acid.

Uranyl fluoride, if it’s suspended in the air, can be inhaled into the lungs and dispersed in the blood stream. It would then be collected into the kidneys and removed through the urine.

If the concentration of uranyl fluoride was high enough, the person could suffer from heavy metal poisoning, the collection of heavy metals like uranium in the body. However, Luxat says, the amount of uranium hexafluoride in the containers would have been too small to create that high of a concentration.

Fluoric acid, on the other hand, is a weak corrosive acid that could irritate the nose, mouth and particularly lungs.

Even an absolute worst-case scenario, where the containers broke and a fire raised the temperature to allow the uranium to react with water as a gas, Luxat says, would not be a dire situation.

“It would occupy a small volume, it’s not as though it’s this big massive cloud that would fall,” he says.

“From the point of view of hazard, the major hazard would be to the first responder who is very close to it, but the amount that would be present, even if he wasn’t wearing a mask, would not cause a problem.”

So what?

Less than four per cent of the cargo moving through the Halifax port are considered dangerous goods, says communications advisor, Lane Farguson, for the Halifax Port Authority. However, a similar incident occurred in 1999 at the port as well, according to a report in the Daily News (Halifax). No uranium hexafluoride was released in that case either.

According to the Canadian Nuclear Safety Commission, the first responders at the recent accident followed the proper emergency procedures set out by the companies licence and the regulation requirements. No one suffered from radiation exposure. The terminal, after being closed for a day, returned to normal operations on Saturday, March 15.

As it was, Luxat says, “there was an event that got kind of blown up, because it was designated a radioactive event.”